Holley carburettor adjustment needed

Hi Rene -

My first picture (handwritten) is how I had my Holley 4150 (List 4609, 735 CFM) set up during the initial phase of my ownership.  The typed data is how the same carb is currently set up.  It starts good, idles good, runs great.

I have drilled my throttle plates (you can see one of the holes in the picture).  All four throttle plates are drilled.

I’m running a 358 ci (351C bored .040” over), a George Pence recommended Bullet cam.  Compression is 10:1.  I am also running the Blue Thunder manifold.

My buddy Wade helped me set this all up, drilled the throttle plates, and we eventually converted this carb to 4-corner idle by drilling, and installing needle valves in the secondary throttle plate..  nevertheless…

It seems to me if your car won’t even run on start up, and doesn’t idle when you open the secondaries all the way up, very small holes (.136”) in your throttle plates will not solve your problems.

I would be thinking about something like ignition timing. But that’s just me.

I hope this information is helpful to you.

Rocky

Hi Rene,

a Holley carburettor is more tolerant than a Weber in terms of adjustments. A new holley is pre-tuned at the factory and runs as it is, and your engine should start, without backfiring, and not stall below 1800 rpm, the choice of jets, nozzles and power valve, cams, etc. .. are for optimized settings. I think it is necessary to recheck the firing order, recheck the connections and the plugs on the carburettor and on the intake pipe, etc ... before drilling holes in the butterflies and returning the secondary back to adjustment of origin.

When I had a weird problem similar to what you are describing - a lot of smoke, could only keep it running at high rpms etc, it was the distributor cap that had been put on crooked. It messed up the rotor. Worth a quick check.

Thank you for your answers, I will check the whole ignition system before changing the carburetor permanently.

You probably have the wrong Holley carb. I am not specifically familiar with the one that you have but it may be that it has the reverse idle system used to get the idle mixture to 14.6 at idle.

A generic 3310 will probably be the easiest for you to use. It's 780cfm and jetted for a 5 to 5.7L v8, so all you should have to do is bolt it on and idle it down.

What you are also describing in the issues with the carb that you are trying to use now is a symptom of a BIG vacuum leak. So check all of the usual places plus the special Pantera places like the power brake vacuum line (all the way to the front).

...If it has Backfired Through the CARB...Just One Time, You have a Blown 'Power Valve' RUBBER Diaphragm on the Primary Metering Block. Too Much Fuel, Flooding Out! If it is a 'Double-Pumper', there is also a Power Valve on the Secondary Metering Block! Check/Test these by Removing and Sucking on them...No Kidding, they should 'Hold' the Vacuum.

MJ

Marlin is correct. Yes on the power valve as the source if the diaphram is ruptured. . It can be blown out by a backfire while starting but it will also flood the engine since the primary bowl will then dump directly into intake manifold.

The current crop of pv's is so bad, of the ones I've tested around 50% are bad right out of the box. Don't suck on them. Get a Moroso pv tester. If you run Holleys, you need one.

SOME new Holleys, but not all,  have a check valve built into the base plate but they are not 100% effective.

There is only one Holley double-pumper that uses a pv in the secondaries. That is a 4181, 850cfm. The others are all just one and it is installed in the primary metering block.

as doug said, it could be a leak on the air intakes for brake assist, pcv, etc. I think the best thing to do first is to disconnect all those hoses that go to the intake and to the Holleyand put caps in place and do a test.

If you don't already have it, a link in french for the Holley settings:

CARBURATEUR AMERICAIN REGLAGE (free.fr)

@dipascale posted:

as doug said, it could be a leak on the air intakes for brake assist, pcv, etc. I think the best thing to do first is to disconnect all those hoses that go to the intake and to the Holleyand put caps in place and do a test.

If you don't already have it, a link in french for the Holley settings:

CARBURATEUR AMERICAIN REGLAGE (free.fr)

Thank you very much for the link, I think it will help me a lot.

I found a first "leak" of depression, the PCV ME Wagner valve which I haven't adjusted yet since it needs a stable idle, I plugged it and it's going a little bit better.
I'm going to check the power valve because in addition to the backfire there are explosions in the exhaust and flames that come out when I keep the engine speed a little high, not when I release the accelerator but while I hold it a little open.

Thank you for all your advice

@rene4406 posted:

Thank you very much for the link, I think it will help me a lot.

I found a first "leak" of depression, the PCV ME Wagner valve which I haven't adjusted yet since it needs a stable idle, I plugged it and it's going a little bit better.
I'm going to check the power valve because in addition to the backfire there are explosions in the exhaust and flames that come out when I keep the engine speed a little high, not when I release the accelerator but while I hold it a little open.

Thank you for all your advice

Yes, the pcv system uses 3-4 inches of vacuum to make it work. I think that you need to hook up a vacuum gauge to help diagnostics.

My vacuum gauge was destroyed by a backfire, I ordered another one.

If you have fire, explosion & flames, it’s not a carburetor problem….

…or a mild vacuum leak!

Especially if it’s coming out the exhaust…

Good luck, have you checked the roll pin in your distributor?

Rocky

as Rocky, if the firing order is OK and if there are flames in the exhaust, I will rather opt  for a lack of advance.

I rechecked the firing order and the connection of the spark plug wires, everything is OK.
It is true that the engine runs better when the vacuum advance is connected and therefore there is more advance.
It seems to me that a really too rich mixture can also cause explosions at the exit of the exhaust when the overflow of gasoline which could not burn in the cylinders comes into contact with the outside air.

Thanks again for all your advice.

@dipascale posted:

as Rocky, if the firing order is OK and if there are flames in the exhaust, I will rather opt  for a lack of advance.

... OR an exhaust valve or valves not seating. What type of camshaft is installed in the engine? Is it a solid lifter or hydraulic lifter?

302 Fords have a history of spark plug wires #7 and # 8 cross firing to the extent that the Ford Engine Assembly Manual shows that they must be separated in the wiring loom on the valve cover. Other Ford engines are not immune from that issue as well.

A problem with the distributor cap such as a crack or the wrong rotor is not out of the question also.

Cam Bullet Racing "GeorgesP" spec, hydraulic roller tappets tuned with very little play, almost like solids.

@rene4406 posted:

Cam Bullet Racing "GeorgesP" spec, hydraulic roller tappets tuned with very little play, almost like solids.

Are you SURE that the valves are closing COMPLETELY? Incorrect valve adjustments are one of the things I would be looking at.

I always prefered solids where I could measure the clearances with a feeler gauge rather then ATTEMPTING to pre-load hydraulic lifters correctly. I always had difficulty with "high performance" hydraulic lifters. They are always a "bear" for me to get right.

I checked the powervalve "by mouth" and it is not destroyed, probably because my carburettor has a protective valve.
I closed the secondary a little so that the progression slot looks like a square.

I increased the lead.

The engine only starts by screwing the idle screw on the primary hands almost fully, when it is running I can loosen the screw up to 1400/1500 rpm, below there is backfire and the engine stalls.

At 1500 revs it takes 36° in advance with the depression connected, backfire below and the engine stalls

The depression is 16 inches, which seems like a lot to me with a cam that has a 285° intake

The engine accelerates slightly when I remove the vacuum gauge and therefore create an additional air intake.

You are kind of isolating this to the carburetor. From your latest post, the carburetor idle circuit is not operating at all.

Is this a new carb or used one being re-applied?

You might want to message Drew Pojedinec on Facebook.

afscarbs.com Web page.

airfuelspart on facebook.

He is one of the most knowledgeable and helpful people that I know of on Holley carburetors. He has mentioned previously that he has brand new Holley carburetors that have had internal problems and incomplete machining and assembly procedures too common to be called rare.

For the moment, try another carburetor.